This invention relates to a process for forming a pattern used in fine fabrication of semiconductors in integrated circuits, large scale integrated circuits, etc. More particularly, the present invention is concerned with a process for forming a pattern which can afford a dry etching-resistant film having a high sensitivity and a high contrast with a simple resist construction.
At present, a projection aligner is mainly used in photolithography. However, when a pattern having a size of the order of submicrons is intended in this method, the contrast of an aerial image which has passed through an optical lens system is lowered, even if the contrast of a mask pattern is high. In particular, this tendency becomes more and more noticeable as the pattern size formed by the fine fabrication of semiconductors is reduced. In order to prevent this lowering in contrast, inorganic photoresist processes using a thin film of a chalcogenide glass have been proposed in, e.g., Oyo Butsuri (Applied Physics), vol. 50, No. 11, 1118-1130 (1981). An example of the inorganic photoresist processes comprises forming a thin silver layer as an upper layer of a chalcogenide (Se-Ge) layer through evaporation or electroless plating, doping the chalcogenide layer with silver through radiation exposure, and forming a pattern by taking advantage of the change in solubility of the chalcogenide layer in an alkali solution or the change in plasma etching resistance of the chalcogenide layer. This process for forming a pattern provides a contrast enhancement effect and enables the formation of a pattern having an extremely high contrast. However, in order to put this process for forming a pattern to practical use, it is necessary to solve the following problems. Specifically, it is necessary to lower by one order the dose of energy required for causing the change in solubility or etching resistance, to enable the film to be formed by a simpler method, e.g., spin coating, and to enhance the thermal stability of chalcogenide.
Meanwhile, since a photoresist which is now in practical use in fine fabrication of semiconductors comprises a mixed layer comprised of a sensitizer and a polymer, the sensitizer is uniformly dispersed in the photoresist layer. Therefore solvent solubilization or insolubilization reaction occurs substantially uniformly throughout the film by radiation exposure, which makes it impossible to improve the contrast. In order to improve the contrast, Japanese Patent Laid-Open No. 10642/1984 proposed contrast enhancement lithography (CEL process) which comprises forming a layer comprised of a non-water soluble polymer and arylnitron as an upper layer of the photoresist to improve the contrast of an image radiated on a resist.
However, the CEL process has a problem that the improvement in contrast leads to an increase in exposure.
Further, an EB (electron beam) lithography resist process used in the production of a mask for photolithography has a problem that a complicated three-layer resist should be applied to prevent the proximity effect caused by the scattering of an electron beam.
As mentioned above, the above-mentioned conventional process, i.e., the inorganic photoresist process, is accompanied by problems such as low sensitivity, necessity of complicated procedures for formation of a photoresist film, and low thermal stability of chalcogenide. Meanwhile, the photoresist process which is now in practical use has a problem that it is hardly expected to enhance the contrast without sacrificing the sensitivity. Further, in the electron beam lithography, the realization of a simplified resist construction is desired.